Expandable/collapsible structures for use in molding articles are relatively abundant in the art. U.S. Pat. No. 3,247,548, which issued to M. R. Fields et al. on Apr. 26, 1966, for example, discloses a radially contractable and expandable die for injection-molding an article having a cavity and a continuous annular radial deformation in that cavity. In particular, the Fields et al. apparatus is expandable to a molding position wherein the expanded apparatus provides a portion of a mold member for injection-molding articles such as plastic caps having internal attachment threads. After injection-molding and sufficient cooling, the apparatus is collapsed and withdrawn from the molded cap without interference with the helical threads formed therein.
Another expandable/collapsible apparatus for forming the mouth-neck portion of a plastic bottle is disclosed in U.S. Pat. No. 4,397,629, which issued to M. Akutsu et al. on Aug. 9, 1983. The Akutsu et al. device comprises an expanding operation zone which is inserted into the mouth-neck portion of a heated preformed plastic parison. The operation zone is thereafter expanded radially thereby drawing the heated plastic against the walls of a surrounding mold. The Akutsu et al. patent also indicates that the outer peripheral wall of the expanding operation zone may be formed with a spiral screw-shaped protuberance to correspond with a screw groove formed in the surrounding mold to thereby form a continuous spiral screw in the mouth-neck portion of the preformed parison. The expanding operation zone is thereafter collapsed and withdrawn from the preformed parison to allow further blow-molding operations not specifically described.
An apparatus for blow-molding a tubular slug of thermoplastic material is also disclosed in U.S. Pat. No. 3,969,060, which issued to Otto Rosenkranz et al. on July 13, 1976. The Rosenkranz et al. equipment includes a split-mold cavity which closes about the heated tubular slug of thermoplastic material constricting the thermoplastic between the mold sections and a central core. Following constriction of the thermoplastic tube, the central core is displaced axially to compress the thermoplastic material in the upper portions of the mold into thread formations formed in the neck-forming area of the mold. After axial compression of the upper end of the tubular slug, the balance of the molded article is formed by introducing blow-molding pressure through the hollow tube of the central core.
Similarly, U.S. Pat. No. 4,115,496, which issued to T. J. Krall on Sept. 19, 1978, concerns a method of molding an internally threaded bunghole in a blow-molded container. As in the Rosenkranz et al. disclosure, the Krall reference describes an externally threaded rigid blow pin assembly which is extended into a plastic parison. A split mold is, thereafter, closed around such parison and rigid blow pin to compression mold the threaded bunghole. Blow-molding pressure is injected into the parison through a blow channel in the rigid blow pin. After blow-molding, the blow pin is unscrewed from the formed threads and the mold is separated to eject the container.
Despite all of the prior work done in this area, there remain problems of inefficiency in incorporating an expandable/collapsible core pin in a blow-molding manufacturing procedure to form a thermoplastic container having a neck-portion with internal attachment means therewithin. With prior art methods and apparatus, one was restricted to awkward multi-step procedures and/or limited to particular container shapes which could be made. Such restrictions resulted in inefficient and expensive manufacturing alternatives.